The invention is directed to orthodontic buccal tubes for securing an arch wire to a tooth. More particularly, the invention is directed to those buccal tubes including a separable cover or cap over an arch wire slot such that the buccal tube may be converted to function as a conventional bracket with an open slot.
Orthodontists often employ on first molars buccal tubes that include a convertible or removable cap or cover to facilitate engaging an arch wire initially. When a second molar is then subsequently to be engaged, the first molar tube cover is removed and the terminal of a new arch wire is extended into a new buccal tube mounted on the second molar, with the first buccal tube then functioning as a conventional bracket with an open arch wire slot.
Use of the convertible buccal tubes is not without difficulty. Placing the arch wire into such a tube can be challenging when a tooth is rotated or canted in relationship to the adjoining bicuspid. The convertible cap may require expensive brazing to the tube body and brazing materials may pose biocompatibility problems, unless the design and materials are carefully selected. A major difficulty has been ensuring that the cap does not separate prematurely. Such premature separation may significantly disrupt an orthodontic treatment plan or require expensive remedial work.
Premature separation is particularly a risk when an arch wire is initially fed into the tube. As noted above, placing the arch wire is difficult and may result in excessive forces being asserted. One prior design flares the mesial entryway to a solid tube to allow greater access to start the wire. This design, however, makes feeding the wire from the first to a second molar, more difficult as the enlarged first molar blinds the operator to the second molar tube. Also, due to its high buccal profile, the prior art buccal tube is uncomfortable for the patient when second molars are erupted
U.S. Pat. No. 4,927,362 secures a convertible cap to an arch wire slot by employing frangible webs along the length of the buccal tube that are sintered into the tube during manufacture. This system provides some reliability, through uniformity of web thicknesses, in resisting premature separation at reasonable manufacturing cost. However, U.S. ""362 does not address the difficulty of inserting large cross sectional wires early in treatment. This issue has become critical with new advanced archwires having superelastic qualities that are increasingly being used by professionals. These wires are flexible and respond to low forces but are characterized by large cross sections.
It is evident that the forces applied by users are much higher at the mesial end than at the distal end of the buccal tube. This is related to the difficulty of large wire insertion that tends to exert higher pressures at the entryway or mesial portion of the cover than at its distal portion. The prior art including US ""362 which employs a uniform web mesially-distally, has failed to adequately secure the convertible cover to the tube body such that premature separation of the cover remains a risk due to those higher mesial forces.
An object of the present invention is to solve the difficulties encountered in employing convertible buccal tubes and to provide a convertible buccal tube having a cover over an arch wire slot that does not prematurely separate.
The invention provides a convertible buccal tube wherein an arch wire slot cover is designed to resist premature separation from the body when subjected to forces that otherwise would cause separation during normal utilization, particularly when an arch wire is initially inserted into the tube arch wire slot.
The convertible buccal tube in a first embodiment of the invention comprises a base attachable to a tooth surface or band on a tooth. The buccal tube further comprises a body fixed to or integral with the base, projecting from the base to define a mesially-distally extending arch wire slot. A cover extends over the slot including mesial-distal seams that are integral between the cover and the body and of a strength selected to facilitate disengaging of the cover from the body but only when an intentional separating force is exerted thereon. The integral seams of the invention are designed and dimensioned to be stronger at their mesial portions than their distal portions such that a larger force must be exerted on the mesial position to initiate disengagement of the cover than required for the distal portion.
A second embodiment of the invention comprises a mesially-distally extending arch wire slot and a convertible cover or cap extending over the slot, wherein the cover is adhered or brazed to the top of the slot using a larger amount of bonding material mesially such that a significantly larger force must be used to disengage the mesial portion of the cover than its distal portion, thus reducing the risk of accidental disengagement. In a preferred design the top of the arch wire slot is provided with parallel mesial-distal extending ledges to accommodate said cap, both ledges and the corresponding cap contact surfaces being mesially-distally tapered, wherein, for example, 50% more bonding material, such as solder, secures the cap to the slot mesially then distally.
Additionally, the convertible cover includes a flared mesial portion such that the covered arch wire slot has a greater opening at its mesial portion than the distal portion which facilitates engagement at the arch wire slot by an arch wire while avoiding the arch wire exerting incidental separating forces on the cover during fitting of an arch wire into a buccal tube arch wire slot.
Preferably, the cover and arch wire slot are formed with integral seams or bonding surfaces that taper mesially-distally wherein the force required to separate the cover is 50% greater at its mesial end than the separation force selected for the distal end of the cover. The flared portion of the cover preferably provides a 50% greater cross-sectional area at the entryway to the arch wire slot. The flared portion is extended only about 25% of the length of the arch wire slot whereby the remaining portion of the combination cover and arch wire slot secure the arch wire in position.